SPICE Simulations
Course This page is for the course ELEC3106 - Electronics and is based on the lectures of Torsten Lehman senior lecturer at the University of New South Wales. Overview Prerequisites The reader of this page is assumed to have a basic understanding of circuit theory, such as that gained from ELEC2134. It is also assumed that the reader is familiar with creating SPICE netlists via the schematic editor and/or writing it directly. SPICE Simulations Simulation Types '''Transient''' The transient analysis is used to view the response of a circuit over time. It does so by solving the system's differential equations for the specified output variable at discrete times. An added feature of this simulation is the Fourier analysis using which you can see the harmonic series of a given centre frequency. Total Harmonic Distortion will appear in the output file if Fourier is enabled. Components The main sources used in transient analysis include: VSIN - A time-warying sinusoid VPULSE - A periodic step source VEXP - An exponential source VPWL - A "Piece-Wise Linear" source which can be used to piece together an arbitrary waveform. All parameters are graphically depicted in the respective Figures. Simulation Parameters Print Step - The time intervals at which the output file is printed to Final Time - The final time on the x-axis Step Ceiling - Maximum time between simulation points Fourier Enabled - Enables a Fourier analysis Centre Frequency - The fundamental frequency when calculation the harmonic series Number of Harmonics - The number of harmonics to include in the series Output Vars - The output variable in Fourier analysis '''DC''' DC Nodal Analysis The node voltages and currents can be viewed in a circuit by using VIEWPOINT and IPROBE respectively. All capacitors are treated as open circuits and all inductors as short circuits. DC Sweep Node voltages and currents can be viewed for a range of given DC input source values. The independent variable is usually a voltage or a current. Components The sources generally used for this analysis are VDC and IDC which allow you to specify a DC voltage and an IC current respectively. Simulation Parameters Name - The name of the source you wish to sweep Start Value & End Value - The values between which the source is swept '''AC''' AC analysis is used to view the response of a circuit in the frequency domain. It is capable of displaying both the magnitude and the phase response of a circuit. It is often used for the small-signal analysis of analogue circuits. Components The main source used for AC analysis is the VAC source which can be set to the desired magnitude and phase. Simulation Parameters AC Sweep Type - Sets the independent axis type out of linear, octave and decade Sweep Parameters - Sets the start and end frequency on the independent axis and also the total number of points to plot Noise Analysis - Using SPICE Models SPICE simulations can only be as good as the models used for the components of a circuit. Better models usually mean increased complexity and computation time, hence the designer is faced with a trade off between accuracy and time. Diode Model Switch Model Voltage-Controlled Voltage Source Op-Amp Models Non-Linear Elements Further Reading It is recommended that the reader visits https://subjects.ee.unsw.edu.au/elec3106/ and reads the lecturers scribbles as an alternative source. See Also